The invention relates to the resin compositions for wire and cable covering materials containing polyphenylene ether resin (abbreviated as PPE). More specifically, the invention relates to resin compositions for wire and cable covering materials that excel in non-halogen, fire retardancy and chemical resistance.
Generally, amorphous resins excel in dimensional precision after injection molding because of their amorphous structural characteristics. Taking advantage of this characteristic, they are widely used in the industrial applications involving large size molding objects where precision assembly is required. However, a consequence of the amorphous structure is organic chemical permeability resulting in weak chemical resistance and easy attacked by oil, organic solvent etc.
On the other hand, crystalline resins have outstanding chemical resistance because of their crystalline characteristic, and are used in applications involve exposure to oil, or organic solvent etc. However, when the crystallization advances in the mold cooling process, crystalline resins are not suitable for large size molded objects because of their low dimensional precision due to the molding shrinkage phenomenon. Although the inorganic fillers, such as glass fibers are added to improve dimensional stability, this results in high density, low ductility impact strength, and different shrinkages in the injection molding flow direction and perpendicular flow, and results in defects like warpage or deformation.
Polyphenylene ether resin is a non-crystalline thermoplastic resin with well-balanced mechanical properties, outstanding electrical properties and low water-absorbing property and excellent dimensional resistance. Moreover, polyphenylene ether resin is compatible with polystyrene resin which is also a non-crystalline thermoplastic resin, and can be modified easily. The resin composition (herein after, abbreviated to PPE/PS resin composition) containing PPE resin and styrene resin has outstanding molding processing characteristics and impact resistance (U.S. Pat. No. 3,383,435), and is widely used for automobile parts, electrical and electronic components. However, as mentioned above, PPE/PS resin composition is amorphous resin, and chemical resistance, specially resistance against aromatic hydrocarbon solvent is poor, e.g. if solvent is exposed to the part which is distorted or the part with residual strain, glaze or crack will occur and will lead to the rupturing of the components. Therefore, there are some restrictions in case of application, such as office equipment with a possibility of adhering to lubricating oil, grease, cleaner, components like computer related equipment (e.g., internal parts, fan motor case, plastic chassis); consumer electronics, business electrical appliances with a possibility of adhering to salad oil, fritter oil and other organic solvents; components of electrical equipment used in an environment of oily smoke, organic gas (e.g. industrial environment, construction-related), such types of applications are avoided. This is considered to be a defect resulting from polyphenylene ether resin being non-crystalline.
Although various experiments have been performed in order to improve the deficiency without affecting the characteristics of PPE/PS resin composition, the technology to improve the chemical resistance has not been obtained. As common prior art, the method of blending PPE/PS composition with crystalline resin, such as polyolefin (e.g., polyethylene, polypropylene, EEA), polyester, nylon etc.; low molecular weight olefin series (e.g. polybutene, ethylene oligomer etc.); and rubber type polymer (e.g., SEBS, SBS, SEPS rubber etc.), has been described. However, in this technology, chemical resistance is improved a little by small amounts of the additives, and if the additives amount is increased in order to demonstrate chemical resistance to a practical level, it brings about a fall in the outstanding mechanical strength, fire retardancy, or causes a delamination phenomenon at the time of the injection molding resulting from inadequate compatibility or causes a defect in dimensional precision at the time of molding in PPE/PS resin composition.
Additionally, alloys of crystalline resin and non-crystalline resin are also known, and as an example, an alloy of polyphenylene ether resin and nylon resin using a compatibilizer was prepared through extrusion compounding and was commercialized. In this technology, polyphenylene ether resin is distributed finely in the matrix of nylon, and the distribution is controlled by the compatibilizer and is called as non-compatible alloy. In other words, by covering polyphenylene ether resin by the nylon matrix, the chemical permeability to polyphenylene ether resin is suppressed, and the chemical resistance is improved. If judged from the view point of nylon, the low dimensional stability resulted from shrinkage during molding of nylon is improved by distributing polyphenylene ether resin in nylon. However, in this technology, the improvement in the dimensional precision is inadequate. It is clear that new technology to improve the chemical resistance of compositions containing polyphenylene ether resin is still needed.
Innovation in technology in recent years, has led to the development of crystalline polystyrene polymer having syndiotactic structure (hereinafter, abbreviated as syndiotactic styrene polymer or syndiotactic polystyrene polymer) in three-dimensional structure (Kokai No. 62-10481 etc.). As a logical extension, experimentation involving blending syndiotactic styrene polymer with various resins has been carried out. Syndiotactic styrene polymer is crystalline and from the styrene molecular structure is highly compatible with polyphenylene ether resin, like conventional atactic styrene polymer, and blend compositions of polyphenylene ether resin and syndiotactic styrene polymer are well-known. Such blend compositions have been described in various patents, such as Kokai no. 01-182344, Kokai no. 01-82350, Kokai no. 02-64140, Kokai no. 02-92948, Kokai no. 02-218724, Kokai no. 03-126743, Kokai no. 05-86296, Kokai no. 05-209098, Kokai no. 05-279530, Kokai no. 06-93151, Kokai no. 06-93153, Kokai no. 07-53815, Kokai no. 07-62175, Kokai no. 07-138433, Kokai no. 07-292184, Kokai no. 07-331003, Kokai no. 08-143699, Kokai no. 08-311196, Kokai no. 09-52958 and Kokai no. 09-52959. Although, various simple properties of alloys of syndiotactic styrene polymer and polyphenylene ether have been described in the above art, very few concrete examples which clarify the improvement in chemical resistance and the synergistic properties of the compositions are given. The improvement in chemical resistance is mentioned in Kokai no. 02-64140, Kokai no. 02-92948, Kokai no. 09-52958 and Kokai no. 09-52959. In the above publications, the chemical resistance is improved by simple addition of syndiotactic styrene polymer and rubber-type elastomer materials to polyphenylene ether resin and increasing the crystalline components, and since nothing has been taken into consideration about maintaining the dimensional precision (which is the feature of amorphous polyphenylene ether resin), these materials lack practical utility. Moreover, the chemical resistance of the compositions has been evaluated by a solvent immersion method involving observation of the appearance of the molded test after it has been immersed into a solvent of fixed quantity for a fixed interval of time. However, the application environments as mentioned above for polyphenylene ether resin is taken into consideration, issues where immersion and contact with solvent is required are not experienced. If a solvent, oil, etc. adheres to the drive circumference of electrical and electronic device by one of the factors during the use, and the issue is limited to the problem of dividing the area with clamping distortion in order to fix the components, polyphenylene ether resin which neither produces glaze nor a crack is desired that excels in chemical resistance when present in the distorted part.
Conventionally, PVC resin is widely used as the resin composition for wires and cables covering material. However PVC resin has low heat resistant temperature of 60° C., and contains halogen as fire retardant, which produces dioxin during combustion and pollutes the environment, and the regulations restricting its use are being tightened.
Additionally, tetrafluoroethylene can be used as the resin composition for wires and cables covering material. However, tetrafluoroethylene is fire retardant but possesses a disadvantage of drip inhibition, and is also processed with difficulty when blended with other resin composition. Moreover, as a consequence of thermal shrinkage, it fails the 5V test of UL94, and there is always a fear of short circuit by destruction of wires and cables covering material in case of a fire.
In addition, since tetrafluoroethylene contains fluoride, it is inherent in the problem of environmental pollution like the above-mentioned PVC resin.
The present invention solves the above mentioned issues with conventional technology, and offers a resin composition for wires and cables covering material, which is excellent in fire retardancy with non-halogen, excels in the chemical resistance, specifically in the distorted area and produces neither glaze nor a crack, and further has excellent compatibility, processability, heat resistance, impact resistance and flexibility.